The invention relates to helicopter power and flight control systems. More particularly the invention relates to simplified propulsion and flight control systems incorporated in a coaxial helicopter vehicle.
Coaxial helicopters have been known for many years. However, because of complexities involved in the control of the cyclic and the collective pitch of rotor blades in a coaxial configuration to give roll, pitch and yaw control, development of this type of aircraft has heretofore been limited. Conventional single rotor designs, having a tail rotor for counteracting the tendency of the airframe to turn with respect to the rotor, and for yaw control, predominate. Nevertheless historically several successful coaxial designs have been developed, for example, by Nikolai Kamov and the Kamov design bureau of the former Soviet Union. The Kamov organization continues to produce coaxial helicopters in the Russian Federation. Other coaxial designs exist, for example a small coaxial pilotless craft developed by United Technologies Corporation, of Hartford Conn. An example of a control system for this later craft is disclosed in U.S. Pat. No. 5,058,824.
An alternative to control of coaxial helicopters by control of the pitch of the blades alone is to make the axis of rotation of the coaxial rotor set tiltable with respect to the airframe, which allows pitch and roll control by shifting the weight of the aircraft with respect to a thrust vector of the coaxial rotor set. Such a system is known, for example that disclosed in U.S. Pat. No. 5,791,592, issued Aug. 11, 1998 to Nolan, et al. Yaw control in the Nolan device is by means of two sets of airfoils which are tiltable with respect to axes roughly parallel and normal to the rotor thrust vector. The airfoil set rotating about axes normal to the thrust vector impinges on the downwash from the rotor set, and creates a reaction force vector tending to yaw the airframe right or left depending on which way the set of airfoils is angled. The second set of airfoils appears to function in a manner similar to a tail rudder in a conventional aircraft, and therefore comes into play when the device has developed significant forward speed, but is less operative in yaw control when the helicopter is hovering at a stationary point or otherwise has very low forward speed. In this simplified system there is no need for cyclic blade pitch control, and there is no collective pitch control. Tilt of the coaxial rotor set, and increasing or decreasing the speed of the rotors, provides pitch, roll and lift control.
It has been recognized that simplifications in design, and the weight and cost savings realized thereby, and commensurate potential advantages in performance for the same cost, argue for a further simplified propulsion and control system in a coaxial rotor helicopter. The invention is directed to this end, and accordingly provides a helicopter propulsion and control system configured for actuating a helicopter airframe having a center of gravity according to control inputs of an operator, comprising: a) a counter-rotating rotor set tiltably coupled to the airframe, the rotor set having an upward thrust vector; b) a power assembly configured to actuate the counter-rotating rotor set, having a center of gravity, and being fixedly coupled to the rotor set so as to be tiltable therewith; and c) a control actuator operatively coupled between the power assembly and the airframe to enable the variable center of gravity of the airframe to move with respect to the center of gravity of the power assembly, and with respect to the thrust vector of the rotor set, whereby pitch and roll of the airframe are controllable by the operator.
In a more detailed aspect, the invention further provides at least one airfoil disposed so as to be in the downwash of said rotor set, said airfoil cooperating with the downwash of the rotor set to create a controllable sideways thrust vector. An airfoil control actuator is operatively coupled between the airfoil and the airframe, configured to change the orientation of the airfoil so as to orient the sideways thrust vector according to control inputs of the operator, whereby yaw of the airframe is controllable by the operator. Two parallel airfoils can be used in tandem to minimize their size, or two counter rotating airfoils can be used, each being disposed on opposite sides of the airframe.
In another more detailed aspect, said power assembly further comprises a prime mover and a gear set. The gear set divides power output from the prime mover into two counter-rotating shafts to drive the respective counter-rotating blades. The gear set can also effect a reduction, whereby rotor rotational speed can be lower than that of the prime mover. The gears can be arranged in different ways, for example a planetary configuration or a beveled configuration. In the latter case a single shaft rotation input, and a dual coaxial counter-rotation shaft output oriented orthogonal to the input can be provided. The prime mover can be any suitable means of energy conversion, such as an internal combustion engine, a turbomachine such as one of a number of turbine engines conventionally used to power helicopters, and an electric motor. The latter example is primarily used for smaller pilotless aircraft, for example in inertially-guided and remote-controlled controlled applications.
In a further more detailed aspect, in one embodiment the power assembly is rotatable with respect to the airframe. In one embodiment the power assembly has a single output shaft, and a first rotor of the counter-rotating rotor set is attached to the power assembly, rotating in a first direction, and a second rotor of the counter rotating rotor set is attached to the single output shaft, and rotates in the opposite direction.
As mentioned, in a further more detailed aspect the invention has application in pilotless aircraft, which may be small, as well as vehicles designed to carry a human operator. A pilotless system where the operator remotely pilots the helicopter can further comprise a transmitter and a receiver cooperating with: i) the actuator(s) disposed between the airframe and the power assembly and ii) an actuator controlling the position of the airfoil, and iii) a power controller controlling rotor speed, to provide control inputs. In another example the operator is a programable electronic guidance and control system operatively connected to the power controller and the rotor control and airfoil actuators, whereby the helicopter is substantially self-controlled. In full-size applications the operator pilots the helicopter onboard the airframe, and in such systems the helicopter system further comprises controls actuatable by the operator carried by the airframe. Such controls can comprise for example a joystick or yoke to provide control of pitch and roll, peddles to control yaw, and a throttle to control rotor speed. A collective pitch control is not required, as the magnitude of the thrust vector of the rotor set is controllable solely by variation of the speed of rotation of the counter-rotating rotor set. However, a collective pitch control can be used in combination with motor speed to control lift in applications where cost is of less concern. Differential collective blade pitch control can be used to provide unbalanced torque in the rotor set to provide yaw control input.
In another more detailed aspect, the actuator disposed between the power assembly and the airframe can further comprise both a pitch actuator disposed to tilt the rotor set and power assembly in a first direction to control pitch, and a roll actuator disposed to tilt the rotor set and power assembly in a second direction to control roll.
Further details, features and advantages will become apparent with reference to the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the features of the invention.